Quick Facts
- Sample: Blood
- Fasting: No fasting required. Stop biotin consumption at least 72 hours prior to collection.
- Turnaround: 2-3 business days. May take longer based on weather, holiday, or lab delays.
What’s Included
- T4 (Thyroxine), Total: Measures the total amount of thyroxine in the blood, including both bound and unbound forms, to help assess thyroid function.
- Thyroxine Binding Globulin (TBG): Measures the primary protein responsible for transporting thyroid hormones in the blood. Helps determine whether abnormal thyroid hormone levels may be related to changes in binding proteins.
- T4-TBG Index: A calculated value derived from total T4 and TBG levels that helps evaluate thyroid hormone status while accounting for variations in thyroid hormone-binding proteins.
Benefits
- Reports total T4, TBG, and a calculated T4-TBG Index together.
- Helps assess how thyroxine relates to its binding protein.
- Supports evaluation alongside other thyroid-related findings.
- Provides both a directly measured and a calculated result.
- Convenient blood draw with no fasting required.
Who Is This Test For?
- Individuals experiencing possible thyroid-related symptoms such as fatigue or weight changes.
- People whose healthcare provider wants to assess T4 and TBG together.
- Individuals monitoring thyroid-related findings as part of ongoing care.
- People whose provider wants context for interpreting total T4 results.
- Individuals following up on prior thyroid-related blood work.
How It Works
- Order Your Test Online
- Visit a Local Lab
- Get Results Online
FAQ
1. What is the purpose of this thyroid test?
This test reports total thyroxine (T4), thyroxine-binding globulin (TBG), and the calculated T4-TBG Index. It may help a healthcare provider evaluate how much thyroxine is present in the blood and how it relates to its carrier protein. This test does not directly measure thyroid function on its own and does not diagnose a condition.
2. When might I consider ordering this test?
You may consider this test if a healthcare provider recommends evaluating total T4 and TBG together, or if you are following up on prior thyroid-related results. It may also be considered by people with possible thyroid-related symptoms as part of an ongoing evaluation.
3. How does this test differ from other thyroid tests?
This test measures total T4 and TBG and calculates the T4-TBG Index from those results. It does not report free hormone levels or thyroid antibodies. TBG reflects the carrier protein for thyroxine rather than thyroid hormone production itself.
4. Do I need to fast or prepare before this test?
Fasting is not required. Stop taking biotin at least 72 hours before collection.
5. How quickly will I get results?
Results are typically available in 2–3 days. Weather, holidays, or laboratory delays may extend this timeframe.
6. How do I interpret the results?
The meaning of total T4, TBG, and T4-TBG Index results depends on your symptoms, medical history, medications, and other laboratory findings. These values are often interpreted alongside other thyroid measurements rather than in isolation. A single result does not confirm or rule out a thyroid condition on its own.
Disclaimer: Reference ranges may vary by laboratory. Listed ranges are general guidelines and may differ from those used by the performing lab. Always consult your healthcare provider for interpretation.
7. What should I do if my results are outside the expected range?
Review your results with a qualified healthcare provider. They can determine whether further evaluation or testing is appropriate based on your health history. Do not stop prescribed medication unless instructed by your healthcare provider.
8. How often should I get tested?
There is no routine testing schedule in the provided information. Follow your healthcare provider’s guidance based on your health needs and prior thyroid-related findings.
Pre-test preparation
No fasting is required. Stop biotin consumption at least 72 hours prior to the collection. Do not stop prescribed medication unless instructed by your healthcare provider.
